Racing fuel doesn't provide more horsepower; it's still just gasoline but with more and different additives to prevent spark knock. It merely allows you to build and tune an engine to develop more horsepower without causing spark knock. As proof, ask any racer how their engine would run on regular pump gas. It won't. Yours will. The computer controls on your car also prevent you from modifying anything in the tuning department.
Car sales is a very competitive numbers game. If GM could have gotten one more inch of headroom, one more foot of cargo space, one more cup holder, or one more horsepower, they would have done it to try to be better than the other car brands.